;;;Run once before a suspect event and once after it to see if the atoms-family has changed.
(DEFUN C:ATOMSDIFF ()
  (IF this_atoms
    (SETQ that_atoms (atoms-family 0) that_atomsn (atoms-family 1))
    (SETQ this_atoms (atoms-family 0) this_atomsn (atoms-family 1))
  )
  (IF (AND this_atoms that_atoms)
    (PROGN
      (SETQ cnt 0)
      (WHILE (AND
               (EQ (NTH cnt that_atoms)(NTH cnt that_atoms))
               (< cnt (LENGTH that_atoms))
             )
        (SETQ cnt (1+ cnt))
      )
      (PRINC "\n")
      (PRINC (NTH cnt that_atomsn))
      (PRINC " = ")
      (PRINC (NTH cnt that_atoms))
      (PRINC)
      (PRINC "\n")
      (PRINC (NTH cnt this_atomsn))
      (PRINC " = ")
      (PRINC (NTH cnt this_atoms))
      (PRINC)
      (SETQ this_atoms NIL
            that_atoms NIL
            this_atomsn NIL
            that_atoms NIL
      )
    )
  )
)